St Petersburg Polytechnic University Journal-Physics and Mathematics最新文献

Based on nuclear algebra of operators acting on spaces of entire functions with θ-exponential growth of minimal type, we introduce the quantum generalized Fourier–Gauss transform, the quantum second quantization as well as the quantum generalized Euler operator of which the quantum differential second quantization and the quantum generalized Gross Laplacian are particular examples. Important relation between the quantum generalized Fourier–Gauss transform, the quantum second quantization and the quantum convolution operator is given. Then, using this relation and under some conditions, we investigate the solution of a initial-value problem associated to the quantum generalized Euler operator. More precisely, we show that the aforementioned solution is the composition of a quantum second quantization and a quantum convolution operator.

Physical, optical and Electron Paramagnetic Resonance (EPR) studies on 15MgO–15BaO–(59.8−x) B₂O₃–(10 + x) TeO₂–0.2Cr₂O₃ (x = 0,10,20,30 mol%) glass samples are reported. EPR spectra exhibited two resonance signals at g = 4.8 and g = 1.98. The resonance signal with large zero field splitting parameter (D) and E/D ≤ 1/3 at g = 4.8 is attributed to isolated Cr³⁺ centers in strongly distorted octahedral sites, whereas the resonance signal at g = 1.98 is assigned to Cr³⁺ centers at axially distorted octahedral sites. The resonance signal at g = 4.26 is assigned to Fe³⁺ ions, which are present in the glass matrix as unwanted impurities. The resonance signal at g = 1.91 indicates the Cr³⁺–Cr³⁺ exchange coupled pairs. The two observed broad optical bands in the optical absorption spectra 16,025 cm⁻¹ and 23,474 cm⁻¹ are assigned to ⁴A_2g(F)→ ⁴T_2g(F) and ⁴A_2g(F)→ ⁴T_1g(F) transitions, respectively. The site symmetry of Cr³⁺ is C_4v or C_3v. Racah parameters, crystal field (D_q) parameters and energy gap are evaluated from the optical spectra. Various other physical parameters like density etc. have also been reported.

The article presents results of 3D numerical simulation of flow and conjugate heat and mass transfer in a model of the TacSat-4 satellite loop heat pipe evaporator. The mathematical model includes the Reynolds-averaged Navier–Stokes equations describing the flow in the liquid and vapor regions, Darcy's law for filtration modeling in the wicks and the energy equation with accurate coupling of connected sub-domains including effects of evaporation on interfaces between the porous and vapor regions. According to the simulation results, the evaporation localizes mainly at the vapor groove corners near the evaporator body. The vapor grooves operate under essentially different conditions, as a result, the flow rates differ by several times. Significant thickening of the evaporator body yields only weak reduction in a level of the grooves’ flow rate non-uniformity.

A uniform formulation of the effective stress tensor symmetrization procedure has been proposed. This form contains the classical additive and multiplicative symmetrization schemes as particular cases. Different options of symmetrization of the effective stress tensor for the unidirectionally damaged material with parallel microcracks and for the bidirectionally damaged material with a system of orthogonal microcracks were compared. The differences in any forms of the effective stress tensor were second-order infinitesimals for low damage levels.

The differences in predictions from considered symmetrization schemes increased with the growth of the damage level and with that of the differences between the eigenvalues of damage.

An identification procedure for anisotropic damage was proposed on the basis of acoustic emission methods and then it was discussed.

The time history of the temperature and the emission measure of the solar flare plasma have been studied relying upon the experimental data on the soft X-rays recorded by the IRIS spectrometer on June 29, 2002 (F1) and March 27, 2003 (F2). F1 was a thermal flare and was not accompanied by hard X-rays. This data analysis revealed that at least two sequential energy-release processes occurred during the F1 event. The F2 event took place behind the limb, so only the top part of the flare loop being the soft X-ray source was recorded by the satellite-based spectrometer. From this data analysis it appeared that fast plasma heating occurred in the initial stage of F2 and then the flare region expanded and the emission measure of flare plasma increased.

The measurement method for determining the motion parameters of the module de-orbiting upon the lunar surface has been suggested. The surface-scattered gammas emitted by a radioactive source are detected using four receptors under uncertainty of the lunar soil's elemental composition. The radar-tracking system in the module allows adapting the gamma-ray altimeter to the lunar-soil composition. A mathematical model of the measuring system has been put forward, and dependences of the gamma flux level on the module altitude and the angle of the slanted surface were obtained. The model makes it possible to analyze the relative position of the radioactive source and the receptors and the composition effect of the substrate. The measurement algorithm uses a recursive neural network, which is proposed to be trained in advance and adapted during the module landing.